The study will determine if the aminoglycoside, gentamicin, has potential as a therapeutic medication for Duchenne muscular dystrophy (DMD). To fulfill this potential, long-term administration of gentamicin must be safe and improve muscle strength. Ideally, it will also increase dystrophin expression with binding at the muscle membrane. The testing paradigm will be a three-arm, six-month, double blind, randomized controlled trial of intravenous (IV) 7.5 mg/kg of gentamicin. Groups 1, 2, and 3 will each have 12 subjects. Group 1 will receive gentamicin every three days, while group 2 will receive drug every seven days. Group 3 subjects receive an IV placebo of 5% dextrose and saline; six subjects infused every three days and six others every seven days. In addition, gentamicin will be used in two short-term, 14-day studies. If either of these groups responds to the 14-day administration by decreasing serum creative kinase (CK), then they become potential candidates for six-month administration. One group of 14-day subjects will have DMD with frameshift mutations. Despite commonly held dogma that aminoglycosides have no effect on this mutation-type, it is important to establish as effect by testing to see if CK drops. A positive outcome potentially reaches more patients, since this is the most common type of DMD gene mutation. Gentamicin will also be used to treat limb girdle muscular dystrophy subjects with stop codon mutations. If the serum CK is lowered, the potential for long-term treatment will be established for these patients.